Journal Article

Seasonality in submesoscale turbulence

Gula, Jonathan, Klymak, Jody M., Ferrari, Raffaele, Callies, Jörn

2015

Overview

Although the strongest ocean surface currents occur at horizontal scales of order 100 km, recent numerical simulations suggest that flows smaller than these mesoscale eddies can achieve important vertical transports in the upper ocean. These submesoscale flows, 1–100 km in horizontal extent, take heat and atmospheric gases down into the interior ocean, accelerating air–sea fluxes, and bring deep nutrients up into the sunlit surface layer, fueling primary production. Here we present observational evidence that submesoscale flows undergo a seasonal cycle in the surface mixed layer: they are much stronger in winter than in summer. Submesoscale flows are energized by baroclinic instabilities that develop around geostrophic eddies in the deep winter mixed layer at a horizontal scale of order 1–10 km. Flows larger than this instability scale are energized by turbulent scale interactions. Enhanced submesoscale activity in the winter mixed layer is expected to achieve efficient exchanges with the permanent thermocline below. Recent numerical simulations suggest that the fronts that develop along the rims of ocean eddies are stronger in winter than in summer. Here, the authors present observational confirmation, which informs how these frontal flows are formed.

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Pub. Group
• Subject: 704/106/829/2737 / Activation / Aerodynamics / Atmospheric gases / Baroclinic flow / Baroclinic instability / Computational fluid dynamics / Computer simulation / Eddies / Energy / Fluxes / Heat exchange / Humanities and Social Sciences / multidisciplinary / Nutrients / Ocean circulation / Ocean currents / Ocean surface / Oceanic turbulence / Primary production / Science / Science (multidisciplinary) / Seasonal variations / Simulation / Surface layers / Thermocline / Turbulence / Upper ocean / Vortices / Winter